Gas turbines with sequential combustion are well known in the art. FIG. 4 shows the general scheme of a gas turbine 25 with sequential combustion. The gas turbine of FIG. 4 comprises a compressor 26, a first combustor 27, a first high-pressure turbine 28, a second combustor 29 and the low-pressure turbine 30. The second combustor 29 reheats the exhaust gas of the first turbine 28 by injecting fuel into the hot gas stream. This is for example done by a mixing arrangement according to FIG. 5, where an actually extending fuel lance 33 is placed in a hot gas channel 31 to inject one or more fuels into the hot gas 32 streaming along an axis 16.
Such a gas turbine reheat system (sequential combustion) proved to excel in achieving very low emissions at high firing temperature in big industrial gas turbines of the type GT24/GT26.
Such combustion system fulfils also a number of stringent requirements such as: low pressure drop, low cooling air consumption, long lifetime, fuel flexibility.
One of the key elements the reheat combustion systems relies on, is the mixing levels achieved between hot gas and fuel before the flame.
The concepts developed up to now provide very good mixing levels and combustion performances.
However, they rely either on high momentum flux ratios, complicated geometries or complex sealing systems between the fuel injector and the hot gas path (see for example documents U.S. Pat. No. 5,645,410, WO 2011/037646 A1, U.S. Pat. No. 5,351,474 A, U.S. Pat. No. 6,192,688 B1, WO 2011/054757, WO 2011/054766 or EP 2 211 109 A1).
The multipoint injection systems described in document WO 2011/054757 and in document WO 2011/054766 provide an effective way to mix the fuel and hot gas with minimal pressure drop, by using a multipoint injection scheme, supported by fluid-dynamic structure generated by dedicated vortex generators or lobes.